package 大数的操作;

import java.math.BigInteger;
import java.util.Scanner;

public class 斐波那契数列 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        BigInteger a[] = new BigInteger[1000000];
        a[0] = BigInteger.valueOf(1);
        a[1] = BigInteger.valueOf(1);
        int n = scanner.nextInt();
        for (int i = 2; i < n; i++) {
            a[i] =a[i-1].add(a[i-2]);
        }

        System.out.println(a[n-1]);

    }
}
